Here is a link to a blog posting by Bob Wells about wilderness self-defense against large predators, such as mountain lions and bears. Bob spent much of his life in Alaska, now lives in wilderness areas in the Western U.S., and has great experience on this particular subject.
The striking thing about Bob’s recommendations, for those who know wilderness from TV, is that he does not recommend firearms of any kind for this purpose. Bob owns and uses such weapons, but he gives practical and experience-based reasons why they fail against attacking mountain lions or bears.
I disagree with Bob on the use of such weapons for self defense against human predators. I respect Bob a great deal for many reasons including his long experience in wild nature. However, my own experience includes living for about twelve years in neighborhoods that other white people typically fear and growing up around violent people. I lost that fear of neighborhoods the same way Bob lost his fear of wild places: by living there. I now see those neighborhoods as much less threatening than do those only see them on the TV news.
What struck me as I read Bob’s posting was that every one of his reasons not to carry firearms for defense against wild animals applies just as well to dangerous people, regardless of location. The ease of carrying, ease and speed of operation, and the issue of wounded animals (or people) becoming more dangerous apply to all situations. I’ll add another issue with humans. Bear spray, mace, or tasers are more easily hidden than any pistol large enough to do damage. The act of carrying any firearm, openly or supposedly concealed, can be construed by the distorted mind of a human predator as a threat. That predator then becomes more likely to act to neutralize the threat. Remember that you do not own the only weapon in any given neighborhood.
Someone mentioned another point in the comments. A bear that has encountered bear spray will be less prone to attacking another person. If that bear is killed and then replaced by another bear, the second bear does not know to fear humans. The same applies to people. If a dangerous person knows from experience that any person, no matter how harmless in appearance, can bring him intense pain and suffering accompanied by humiliation in the eyes of his peers, that is a deterrent. Based on my own experience, I believe it’s a better deterrent than the threat of death. Those predators are mostly addicts, and many of them would welcome death. Pain and humiliation are another matter.
In short, Bob Wells has great experience and intelligence in the wilderness. Pay attention to his know-how with regard to four-legged predators. I have enough experience in places with dangerous humans (almost anywhere, realistically) to make a credible statement that Bob’s ideas apply there as well.